S23 to N2: Add Mother and Main names for non-Namco customized PCBs, not the chassis name

[soundsnow]

Starting with System 246 and System 23, all you add are almost chassis names, but they have Mother PCB or Main PCB names. I don't know much about System N2, if it's not a custom motherboard from Bandai Namco, it doesn't matter. It would be impossible to complete a list of System 256 games classified this way. As far as I know, there are only three different motherboards for System 256, S256, S256B and SS256. The first part System 246 is the chassis name, and the second part System 147 becomes the motherboard name. This one is unreasonable.